To achieve the high data rate requirement of the Long Term Evolution Advanced (LTE-A) of the 3.sup.rd Generation Partnership Project (3GPP), it may be beneficial to increase the transmission bandwidths over those that can be supported by a single carrier. Therefore, a carrier aggregation (CA) is proposed. By using the CA, it may be possible to utilize more than one carrier and in this way increase the overall transmission bandwidth. These channels or carriers may be contiguous elements of the spectrum, or they may be in different bands.
Moreover, an unlicensed band may be utilized along with or instead of a costly licensed spectrum. The unlicensed, license exempt or a license-free spectrum may also be called as a shared spectrum. Interesting shared band opportunities may comprise e.g. the industrial, scientific and medical (ISM) bands and TV white spaces.
However the use of the unlicensed bands may be cumbersome due to regulations and because interference to other systems utilizing the shared band must be controlled, for example. Thus, finding free carriers for the carrier aggregation from the scarcity of available interference free carriers on the shared band may be problematic. Therefore, a solution for improving the carrier aggregation communication efficiency on a shared band is needed, for example.